O.K. i have an 86 trans am and just recently replaced the heater core myself. First thing you do is drain all the coolant from the engine. disconnect battery. the heater core is located on the passenger side inside the lower dashboard. You will have to unscrew the lower dashboard and either let it hang down or pop out the convenience light to make more room to move it out of the way, i would pop out the light. Once you have it down there will be a rectangular black box like covering, you will need to unscrew this, note that it would be best to use a long socket extension as there are screws at the topback, use a flashlight first to check out where all the screws are, there are about 5 or 6 if i recall. Once you have the screws off pull the recantangular shaped box towards you and down. Might have to play with it to get it out. Once off, there is another black like box with a metal plate on it. Unscrew the metal plate and unscrew the black like box. Again there are screws that are hard to see so use a flashlight first to check out where all the screws are whether at the back top or sides. I believe again there are 5 or 6. Once you have the screws out pull the box from the left side towards you to release the clip that is attached to the heater core, you cant see the clip but the box covering is attached to the heater core so you will have to play with the box covering to get it to come off, you will be able to see the exposed heater core once the box is off. Next, disconnect the hoses in the engine bay against the firewall, the two inlet outlet hoses. You can't miss them, they are the only ones going into the firewall on the passenger side. If they are hard to pull off they maybe melted on or the pressure is keeping them on. You will have to cut them off and get 2 new heater hoses. Don't bother trying to pull them off if they are stuck, i tried, waste of time and frustration. Use a knife to slit the hoses at the firewall, this will release the pressure. Once you have the hoses off the heater core tubes at the firewall, go back inside the car and pull on the heater core towards you to pull it out. Put in the new heater core, if the tubes on the new heater core dont go through the firewall holes because they are to far apart, bend them in slightly, you will hear some metal creaking but this is the only way, I did this and have had no problems. Attach your old or new heater hoses again in the engine bay to the new heater core tubes that come through the firewall and clamp them and clamp them at the engine block as well. Put new coolant in the car. reattach battery. Start car to get new coolant circulated and look at the heater core to make sure there are no leaks as well as the hoses. let the engine warm up for 5 to 10 minutes then turn off engine. Go back into the car and start to put the black box with clip back into place. Note that this part is tricky as i could get the black box clip onto the heater core but the long bar clip at the end of the black box would not let me screw the box into place so i unscrewed it from the black box and just had the one clip from the box on the heater core, to get it to screw into place. Once you have this box in place re attach the metal plate and then put the other retangular box back in place with screws and then reattach your dashboard. Check the coolant level again and add more coolant if necessary. Will need to start car again. , can be frustrating but there are also manuals out there to help.
ok,, i got the houseing off that houses the heater core i took the screws out that hold the clip for the heater core,, but when i go to pull it out it seem slike its bending the tubes, now when i put my new one in will it be ok or will it bend the tubes and wreck them or just be careful and gentle with it or does the days have to come off?? i got the top dash piece off the basket for the stereo deck,, and the housing underneath,, now i am concerend whether this method will work without damaging anything.